Recovery boilers, such as the chemical recovery boilers used in the pulp and paper industry, generally include a plurality of air ports located around the base of the boiler. As a side effect of the process, a build up of slag in the ports occurs which reduces oxygen flow to the boiler thereby impairing the efficiency of the whole pulp and paper making process. Automatic port cleaning systems are typically used to remove the slag that accumulates in the ports at the base of the boiler. FIG. 1 shows an example of a prior art automatic port cleaning system. These automatic systems conventionally include multiple elongated cylindrical rods 102 (cleaning rods) which are mounted in parallel on the outside wall of the boiler (by way of faceplate 104) and which are operated in a periodic reciprocating manner (typically by a pneumatic cylinder 105) so that the tip 106 of each cleaning rod is repeatedly moved into the air port opening and then retracted to free the ports of debris.
These cleaning rods are each journaled in, and reciprocated through, a pair of coaxial bushings which in turn are supported by steel tubes (fulcrum tubes 108). These cleaning rods are typically made from stainless steel and are about 1 inch diameter and reciprocate 8 inches. When the cleaner is retracted from the port openings, a portion of the cleaning rods is exposed to the harsh external recovery boiler environment and, as a result, dirt, fuel oil, black liquor (the fuel fired in a recovery boiler), salt cake dust (sodium sulfate used in the process), or other debris can form on the cleaning rods themselves. In turn, the buildup of material on the cleaning rods can cause premature wear or damage of the bushings. One method of preventing such damage is to protect the cleaning rods from exposure to the boiler environment by employing a type of collapsible elastomeric bellows 110 which prevent material from contacting the cleaning rods. Unfortunately, this solution is not ideal because the bellows material breaks down quickly in the harsh environment around the boiler. When the bellows fail, any foreign material that builds up on the exterior of the cleaning rods is drawn into the fulcrum tubes where it can wear away at the bushings. Replacement of the bellows requires time-consuming disassembly of the mechanism.
Another option is the use of a rod scraper to remove material that collects on the cleaning rods. Prior art rod scrapers are typically mounted at the end of the fulcrum tubes (in the same general area as the bellows shown in FIG. 1) so that they clean and scrape the sides of the cleaning rods as the rods are reciprocated by the pneumatic cylinder. These prior art scrapers are generally made from soft metal or plastic compounds. Prior art rod scrapers have been used to clean the cleaning rods with some success.
There are a significant number of problems with prior art scrapers, however, that are addressed by the current invention. First, prior art scrapers such as the ones commonly used, have a closed ring shape and completely encircle the cleaning rod. Disassembly of the mechanism is required to install or replace the rod scraper. For automatic port cleaners, and many other similar applications, this is very time-consuming.
Another common problem is that normal use of the cleaning rods often involves excessive lateral movement of the cleaning rods beyond what the rod scrapers can accommodate. In the typical automatic port cleaner, the working clearances between the bushings (in the fulcrum tubes) and cleaning rods may be relatively large, allowing play between the rod and bushings. The bushings are also designed to allow for significant wear, which creates larger than normal clearances after usage. This means the cleaning rods may be working offset from the original centerline of the bushings. In other words, the rod scraper should be able to accommodate significant bushing wear resulting in significant lateral displacement of the rod from its original position. Prior art rod scrapers do not allow for significant lateral displacement.
Another common problem is that the rods are typically lubricated using a grease gun that can create significant hydraulic pressure inside the fulcrum tubes. A closed-ring type rod scraper, mounted in a sealed housing, will tend to contain the hydraulic pressure developed by the grease gun. This can result in the scraper or housing popping off the end of the fulcrum tube.
Accordingly, there is a need for an improved rod scraper that avoids these problems of the prior art. Embodiments of the present invention address these problems as described below and in the appended claims.